Plunger and accumulator

ABSTRACT

A work roll balance plunger and accumulator for the mill stands of a rolling mill which is positioned in at least two of the work roll chocks so as to support the upper work roll chocks to substantially reduce hydraulic shock pressure drops or peaks during the expansion or compression of the mill stand as rolling strip enters or leaves, respectively.

O Umted States Patent 1151 3,659,447 Naber et al. 14 1 May 2, 1972 54] PLUNGER AND ACCUMULATOR 2,430,410 11/1947 Pauls ..72/24s ,678,4 5 1954 S h k al. ..72 [72] inventors: Richard E. Naber; William D. Hamilton, 2 65 l c MC at /245 both of Middletown, Ohio [73] Assignee: Armco Steel Corporation, Middletown, Primary Examiner Mmon Mehr Ohm Attorney-Melville, Strasser, Foster & Hoffman [22] Filed: Aug. 25, 1970 [2]] Appl. No.: 66,674

[57] ABSTRACT [52] US. Cl ..72/240, 72/245, 72/246 A work roll balance plunger and accumulator for the mill [51 ..B2lb 31/20, B2lb 31/32 stands of a rolling mill which is positioned in at least two of the Field of Search 245, 246 work roll chocks so as to support the upper work roll checks to substantially reduce hydraulic shock pressure drops or [56] References Cited peaks during the expansion or compression of the mill stand as UNITED STATES PATENTS rolling strip enters or leaves, respectively.

2,027,283 1/ 1936 McFadden ..72/246 5 Claims, 7 Drawing Figures PATENTEDHAY 2 m2 INVENTOR/S P/cl/A/w E. Mass/2 VV/LL/AM D. HAMILTON,

m k adan, fil z M$7wzaw ATTORNEYS PLUNGER AND ACCUMULATOR BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to mills for rolling strips and similar flat materials of great widths and comparatively thin gauges, in long lengths, using backed-up rolls of small diameter.

2. Description of the Prior Art.

The lower and upper work rolls in a mill stand of a rolling mill are mounted in chocks in a frame with the lower work roll being fixed and the upper work roll moving upwardly and downwardly with respect thereto on plungers, which are connected to a work roll balance hydraulic system, positioned in one of the work roll chocks. Since the work rolls of the mill stand are set a prefixed distance apart which is substantially less than the thickness of the incoming rolling strip, a tremendous force is exerted by the rolling strip on the upper work roll when it enters the mill stand, reducing the force on the plungers which support the upper work roll and causing a tremendous hydraulic shock pressure drop in the work roll balance hydraulic system. Similarly, when the rolling strip leaves the work rolls of the mill stand, there is a sudden loss of the force of the rolling strip against the upper work roll, creating a large force on the plungers which support the upper work roll and causing a tremendous hydraulic shock pressure peak in the work roll balance hydraulic system. For example, it is not unusual to experience shock pressure peaks from 6,000 psi. to 7,000 psi. where the normal static pressure of the work roll balance hydraulic system is 1,800 psi.

The art has been generally unsuccessful in developing any practical method or apparatus which will substantially reduce the aforementioned shock pressure drops and peaks. For example, the art has sought to solve this problem by placing accumulators in the hydraulic lines external of the mill stands. However, this has proven to be unsuccessful because by the time the pressure drops and peaks have reached the accumulators they have already damaged the work roll balance hydraulic system.

SUMMARY OF THE INVENTION The present invention provides a work roll balance plunger and accumulator for the mill stands of a rolling mill. In practice, at least one plunger and accumulator is positioned in substantially a vertical bore in each of the lower work roll chocks or in each of the upper work roll chocks, or in both the lower and upper work roll chocks, so as to support the upper work roll chocks.

Briefly, the work roll plunger and accumulator comprises a body which is provided with a cylindrical cavity, the lower end of the cavity being open and communicating with a reservoir of hydraulic fluid. A sealed piston is located within the cavity. The sealed piston is loaded by compressed gas on the piston side away from the hydraulic fluid. Accordingly, the portion of the cavity on the hydraulic fluid side of the sealed piston may contract or expand during the expansion or compression of the mill stand as the rolling strips enter and leave, respectively. This substantially reduces the hydraulic shock pressure drops and peaks in the work roll balance hydraulic system.

In a preferred embodiment,the work roll balance plunger and accumulator is made of mild steel with a bronze overlay on the outside bearing surface. Additionally, a charging valve is located in the closed end of the body to load the piston side of the sealed piston with compressed gas.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows the general arrangement of a mill stand in front elevation.

FIG. 2 is an enlarged schematic representation showing a rolling strip passing through a set of backed-up work rolls.

FIG. 3 is an enlarged plan view taken on the line 3-3 of FIG. 1.

FIG. 4 is an enlarged front elevation showing the backed-up work rolls and work roll chocks utilizing the plunger and accumulator of the present invention.

FIG. 5 is an enlarged cross sectional view through the plunger and accumulator of the present invention.

FIG. 6 is a top plan view of the plunger and accumulator of FIG. 5.

FIG. 7 is a bottom plan view of the plunger and accumulator of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Mills for rolling strips and similar flat material of greath widths and comparatively thin gauges, in long lengths, include a plurality of mill stands 10 as shown in FIG. I. In practice, each mill stand 10 includes a frame having at least two vertical columns and horizontal cross members forming rigidly connected beams therebetween. The entire frame may be formed of one piece of metal whereby the bending resistance of the columns and the increased rigidity of the beams helps to decrease the deflection of the working rolls produced by the roll pressure.

As shown in FIGS. 24, upper and lower work rolls 12 and 14 are mounted in the mill stand 10, the ends of the work rolls being mounted in the upper chocks l6 and the lower chocks 18 in the vertical columns of the mill stand. Upper and lower back-up rolls 20 and 22 for the upper and lower work rolls 12 and 14, respectively, are also provided. However, it should be clearly understood that the plunger and accumulator of the present invention may be utilized in two high mill stands which are provided with upper and lower work rolls but not with upper and lower back-up rolls.

Appropriate means, such as a lead spindle 24a, a pinion stand 24b, two universal spindles 24c (only one shown) and two coupling boxes 24d (only one shown) communicate with drive means, such as a drive motor (not shown) to drive the work rolls l2 and 14.

For purposes of an exemplary showing only, FIGS. 2 and 3 disclose at least one work roll balance plunger and accumulator 26 of the present invention secured in a vertical bore 28 in each of the lower work roll chocks 18. However, it should be understood that according to the present invention at least one plunger and accumulator may be positioned in substantially a vertical bore in each of the lower work roll chocks, or in each of the upper work roll chockspr in both the lower and upper work roll chocks, so as to support the upper work roll chocks. While the plunger and accumulators of the present invention are normally positioned in the lower work roll chocks, as they are then held in place by gravity when the work rolls are changed, when they are positioned in the upper work roll chocks, suitable means may be provided to retain them therein when the work rolls are changed.

As best seen in FIGS 5-7, the work roll balance plunger and accumulator 26 includes a body or housing 29 which is provided with a cylindrical cavity 30. The cylindrical cavity 30 is closed at one end 30a by a charging valve 32 and an end cap 35, and is open at the other end 30b so as to communicate with a reservoir of hydraulic fluid 33 through the opening 37 in the retainer cap 34. A sealed piston 36 'is provided within the cavity 30. The sealed piston 36 is loaded by compressed gas on the piston end 30a away from the hydraulic fluid through the charging valve 32.

In practice, best results have been obtained when at least two plunger and accumulators 26 are positioned in each of the lower work roll chocks 18. Additionally, it has been found that best results are obtained when the plunger and accumulators 26 are made of mild steel with a bronze overlay on the outside bearing surface. Any suitable seal means 39 is provided in the annular groove 41 of the work roll balance plunger and accumulator 26.

During the operation of a rolling mill when a rolling strip 40 enters the work rolls l2 and 14, a tremendous force is exerted by the rolling strip 40 on the upper work roll 12 because the work rolls have been set a prefixed distance apart which is substantially less than the thickness of the incoming strip. This action reduced the force on the plunger and accumulators 26 which support the upper work roll 12, and thus reduces the pressure in the hydraulic fluid reservoirs 33. As opposed to the solid work roll plungers of the prior art, the plunger and accumulators 26 of the present invention substantially reduce the hydraulic shock pressure drops because the sealed pistons 36 tend to move downwardly to compensate for the reduced pressure in the fluid reservoirs 33.

Similarly, when the rolling strip 40 leaves the work rolls l2 and 14 of the mill stand 10, there is a sudden loss of the force of the rolling strip against the upper work roll 12. This action creates a large force on the plunger and accumulators 26, and thus increases the pressure in the fluid reservoirs 33. As opposed to the solid upper work roll plungers of the prior art, the plunger and accumulators 26 of the present invention substantially reduce the hydraulic shock pressure peak because the sealed pistons 36 tend to move upwardly to compensate for the increased pressure in the fluid reservoirs 33.

In practice, it has been found that utilization of the plunger and accumulators 26 of the present invention in a mill stand will reduce the more critical hydraulic shock pressure peaks in the range of 6,000 to 7,000 p.s.i. to the range of 2,000 to 2,200 p.s.i. where the normal static pressure of the work roll balance hydraulic system is 1,800 p.s.i.

While certain preferred embodiments of the invention have been specifically illustrated and described, it is understood that the invention is not limited thereto, as many variations will be apparent to those skilled in the art, and the invention is to be given its broadest interpretation within the terms of the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a mill stand of a rolling mill for rolling strips and similar flat material of great widths and comparatively thin gauges, in long lengths, of the type having upper and lower work rolls, the ends of said work rolls being mounted in chocks in said mill stand, the improvement, in combination therewith, comprising at least one work roll balance plunger and accumulator positioned in a substantially vertical bore in at least two of said work roll chocks so as to support the upper work roll chocks, each of said work roll balance plunger and accumulators having a body which is provided with a cylindrical cavity, the lower end of said cavity being open and communicating with a reservoir of hydraulic fluid, and a sealed piston within said cavity, said sealed piston being loaded by compressed gas on the piston side thereof away from the hydraulic fluid, whereby the portion of the cavity on the hydraulic fluid side of said sealed piston may contract or expand during the expansion or compression of said mill stand when a strip enters or leaves respectively, so as to substantially reduce hydraulic shock pressure drops or peaks.

2. The mill stand according to claim 1, wherein said work roll balance plunger and accumulator is made of mild steel with a bronze overlay on the outside bearing surface.

3. The mill stand according to claim 1, wherein the piston side of said sealed piston is loaded with compressed gas through a charging valve located in the closed end of said body.

4. The mill stand according to claim 1, wherein at least one work roll balance plunger and accumulator is positioned in each of said lower work roll checks.

5. The mill stand according to claim 1, wherein at least one work roll balance plunger and accumulator is positioned in each of said upper work roll chocks. 

1. In a mill stand of a rolling mill for rolling strips and similar flat material of great widths and comparatively thin gauges, in long lengths, of the type having upper and lower work rolls, the ends of said work rolls being mounted in chocks in said mill stand, the improvement, in combination therewith, comprising at least one work roll balance plunger and accumulator positioned in a substantially vertical bore in at least two of said work roll chocks so as to support the upper work roll chocks, each of said work roll balance plunger and accumulators having a body which is provided with a cylindrical cavity, the lower end of said cavity being open and communicating with a reservoir of hydraulic fluid, and a sealed piston within said cavity, said sealed piston being loaded by compressed gas on the piston side thereof away from the hydraulic fluid, whereby the portion of the cavity on the hydraulic fluid side of said sealed piston may contract or expand during the expansion or compression of said mill stand when a strip enters or leaves respectively, so as to substantially reduce hydraulic shock pressure drops or peaks.
 2. The mill stand according to claim 1, wherein said work roll balance plunger and accumulator is made of mild steel with a bronze overlay on the outSide bearing surface.
 3. The mill stand according to claim 1, wherein the piston side of said sealed piston is loaded with compressed gas through a charging valve located in the closed end of said body.
 4. The mill stand according to claim 1, wherein at least one work roll balance plunger and accumulator is positioned in each of said lower work roll chocks.
 5. The mill stand according to claim 1, wherein at least one work roll balance plunger and accumulator is positioned in each of said upper work roll chocks. 